Past Missions

the first successful probe to flyby Venus in December
of 1962, and it returned information which confirmed that Venus is
a
very hot (800 degrees Fahrenheit, now revised to 900 degrees F.)
world
with a cloud-covered atmosphere composed primarily of carbon
dioxide.

launched on November 5, 1964, was lost when its protective
shroud failed to eject as the craft was placed into interplanetary
space. Unable to collect the Sun's energy for power from its solar
panels, the probe soon died when its batteries ran out and is now
in
solar orbit. It was intended for a Mars
flyby with Mariner 4.

the sister probe to Mariner 3, did reach Mars in 1965 and
took the first close-up images of the Martian surface (22 in all)
as it
flew by the planet. The probe found a cratered world with an
atmosphere
much thinner than previously thought. Many scientists concluded
from
this preliminary scan that Mars was a "dead" world in both the
geological and biological sense.

Mariner 9, the sister probe to Mariner 8 which failed on
launch,
became the first craft to
orbit Mars in 1971.
It returned information on the Red Planet that no
other probe had done before, revealing huge volcanoes on the
Martian
surface, as well as giant canyon systems, and evidence that water
once
flowed across the planet. The probe also took the first detailed
closeup
images of Mars' two small moons,
Phobos and Deimos.

Pioneer 10 was the first spacecraft to flyby
Jupiter in 1973.
Pioneer 11
followed it in 1974, and then went on to become the first probe to
study Saturn in 1979.
The Pioneers were designed to test the ability of spacecraft to
survive passage
thru the asteroid belt and Jupiter's magnetosphere. The
asteroid belt was easy,
but they were nearly fried by ions trapped in Jupiter's
magnetic field. This
information was crucial to the success of the Voyager
missions.

Pioneer 11's RTG power supply is dead. Its last communication
with Earth
was in November 1995.
Pioneer 10 is still functioning (barely) but is no longer being
tracked regularly due to budget cutbacks. The last data was
received from
it on 1997 March 31.
They are heading off into interstellar space, the first craft
ever to do so.

As the first two spacecraft to leave our solar system,
Pioneer 10 & 11 carry a graphic message in the form of a 6- by
9-inch gold anodized
plaque
bolted to the spacecraft's main frame.

used Venus as a gravity assist to Mercury in 1974. The probe
did return the first close-up images of the Venusian atmosphere in
ultraviolet, revealing previously unseen details in the cloud
cover,
plus the fact that the entire cloud system circles the planet in
four
Earth days. Mariner 10 eventually made three flybys of Mercury
from 1974
to 1975 before running out of attitude control gas. The probe
revealed
Mercury as a heavily cratered world with a mass much greater than
thought. This would seem to indicate that Mercury has an iron core
which
makes up 75 percent of the entire planet.

Viking 1 was launched from Cape Canaveral, Florida on August
20, 1975 on
a TITAN 3E-CENTAUR D1 rocket. The probe went into Martian
orbit on June
19, 1976, and the lander set down on the western slopes of Chryse
Planitia on July 20, 1976. It soon began its programmed search for
Martian micro-organisms (there is still debate as to whether the
probes
found life there or not), and sent back incredible color panoramas
of
its surroundings. One thing scientists learned was that Mars' sky
was
pinkish in color, not dark blue as they originally thought (the
sky is
pink due to sunlight reflecting off the reddish dust particles in
the
thin atmosphere). The lander set down among a field of red sand
and
boulders stretching out as far as its cameras could image.

Viking 2 was launched on September 9, 1975, and arrived in
Martian orbit
on August 7, 1976. The lander touched down on September 3, 1976 in
Utopia Planitia. It accomplished essentially the same tasks as its
sister lander, with the exception that its seismometer worked,
recording
one marsquake.

The last data from Viking (Lander 1) made its final transmission to
Earth Nov. 11, 1982. Controllers at JPL tried unsuccessfully for
another six and one-half months to regain contact with Viking Lander
1. The overall mission came to an end May 21, 1983.

An interesting side note: Viking 1's lander has been designated
the
Thomas A. Mutch Memorial Station in honor of the late leader of
the
lander imaging team. The National Air and Space Museum in
Washington,
DC is entrusted with the safekeeping of the Mutch Station Plaque
until
it can be attached to the lander by a manned expedition.

Voyager 1 (image at top) was launched September 5, 1977, and
flew past
Jupiter on March
5, 1979 and by Saturn
on November 13, 1980. Voyager 2 was launched
August 20, 1977 (before Voyager 1), and flew by Jupiter on August
7,
1979, by Saturn on August 26, 1981, by Uranus
on January 24, 1986, and
by Neptune on August 8, 1989.
Voyager 2 took advantage of a rare
once-every-189-years alignment to slingshot its way from outer
planet to
outer planet. Voyager 1 could, in principle, have headed towards
Pluto,
but JPL opted for the sure thing of a Titan close up.

Between the two probes, our knowledge of the 4 giant planets,
their
satellites, and their rings has become immense. Voyager 1&2
discovered
that Jupiter has complicated atmospheric dynamics, lightning and
aurorae.
Three new satellites were discovered. Two of the major
surprises were that Jupiter has rings and that
Io has active sulfurous
volcanoes, with major effects on the Jovian magnetosphere.

When the two probes reached Saturn, they discovered over 1000
ringlets
and 7 satellites, including the predicted shepherd satellites that
keep
the rings stable. The weather was tame compared with Jupiter:
massive
jet streams with minimal variance (a 33-year great white spot/band
cycle
is known). Titan's atmosphere was smoggy.
Mimas's appearance was
startling: one massive impact crater gave it the Death Star
appearance.
The big surprise here was the stranger aspects of the rings.
Braids,
kinks, and spokes were both unexpected and difficult to explain.

Voyager 2, thanks to heroic engineering and programming
efforts,
continued the mission to Uranus and
Neptune.
Uranus itself was highly
monochromatic in appearance. One oddity was that its magnetic axis
was
found to be highly skewed from the already completely skewed
rotational
axis, giving Uranus a peculiar magnetosphere. Icy channels were
found on
Ariel, and
Miranda was a bizarre patchwork
of different terrains. 10
satellites and one more ring were discovered.

In contrast to Uranus, Neptune was found to have rather active
weather,
including numerous cloud features. The ring arcs turned out to be
bright
patches on one ring. Two other rings, and 6 other satellites, were
discovered. Neptune's magnetic axis was also skewed.
Triton had a
canteloupe appearance and geysers. (What's liquid at 38K?)

If no unforeseen failures occur,
we will be able to maintain communications with both spacecraft
until at least the year 2030.
Both Voyagers have plenty of hydrazine fuel -- Voyager 1 is
expected
to have enough propellant until 2040 and Voyager 2 until 2034.
The
limiting factor is the RTGs (radio-isotope thermal generators).
The power output from the RTGs is slowly
dropping each year. By 2000, there won't be enough power for
the UVS
(ultraviolet spectrometer) instrument. By 2010, the power will
have
dropped low enough such that not all of the fields and
particles instruments
can be powered on at the same time. A power sharing plan will
go into
effect then,
where some of the F&P instruments are powered on, and others
off.
The spacecraft can last in this mode for about another 10
years, and after
that the power will probably be too low to maintain the
spacecraft.

Giotto was launched by an Ariane-1 by ESA on July 2 1985, and
approached
within 540 km +/- 40 km of the nucleus of
Comet Halley on March 13,
1986. The spacecraft carried 10 instruments including a multicolor
camera, and returned data until shortly before closest approach,
when
the downlink was temporarily lost. Giotto was severely damaged by
high-speed dust encounters during the flyby and was placed into
hibernation shortly afterwards.

In April, 1990, Giotto was reactivated. 3 of the instruments
proved
fully operational, 4 partially damaged but usable, and the
remainder,
including the camera, were unusable. On July 2, 1990, Giotto made
a
close encounter with Earth and was retargeted to a successful
flyby of
comet Grigg-Skjellerup on July 10, 1992.

a joint mission of the Ballistic Missile Defense Organization
(formerly SDIO) and NASA to flight test sensors developed by
Lawrence
Livermore for BMDO. The spacecraft, built by the Naval Research
Lab, was
launched on January 25 1994 to a 425 km by 2950 km orbit of the
Moon for a 2
month mapping mission. Instruments onboard include UV to mid-IR
imagers,
including an imaging lidar that may
be able to
also obtain altimetric
data for the middle latitudes of the Moon.
In early May the spacecraft
was to have been sent out of lunar orbit toward a flyby
of the asteroid 1620 Geographos
but a failure prevented the attempt.

Ground controllers have regained control of the spacecraft,
however.
Its potential future mission is being considered.

Mars orbiter including 1.5 m/pixel resolution camera.
Launched 9/25/92 on a Titan III/TOS booster. Contact was lost with
MO on
8/21/93 while it was preparing for entry into Mars orbit. The
spacecraft
has been written off
(postmortem
analysis).
Mars Global Surveyor,
a replacement mission to achieve
most of MO's science goals, has been very successful.

Launched in May 1989, Magellan
has mapped 98% of the surface of Venus
at better than 300 meter resolution and obtained a
comprehensive gravity field map for 95 percent of the planet.
Magellan recently executed an 80-day aerobraking program to
lower and
circularize its orbit. Magellan has
completed its radar mapping and gravity data collection. In
the fall of
1994, just before it would have failed due to deterioration in
its solar
panels, Magellan was deliberately sent
into Venus' atmosphere to further study
aerobraking techniques which can make major savings in fuel for
future
missions.

a large orbiter with
several landers originally known as Mars 94.
Launch failed 1996 November 17.
(The original Mars 96 was known for a while as Mars 98 and then
cancelled.)
(more info from MSSS and
from IKI
(Russia))

Ongoing Missions

Voyager 1 and 2

still operational after more than 15 years in space and are
traveling out of the Solar System. The two Voyagers are expected to
last until at least the year 2015 when their radioisotope
thermoelectric generators (RTG) power supplies are expected for fail.
Their trajectories give negative evidence about possible planets
beyond Pluto. Their next major scientific discovery should be the
location of the heliopause.
Low-frequency radio emissions believed to originate at the heliopause
have been detected by both Voyagers.

Both Voyagers are using their ultraviolet spectrometers to map
the heliosphere and study the incoming interstellar wind. The cosmic
ray detectors are seeing the energy spectra of interstellar cosmic
rays in the outer heliosphere

Voyager 1 has passed the Pioneer 10
spacecraft and is now the most distant human-made
object in space.

Jupiter
orbiter and atmosphere probe, now in Jupiter orbit.
It will make extensive surveys of the Jovian moons and the
probe has
descended into Jupiter's atmosphere to provide our first direct
evidence of the interior of a gas giant.

Galileo has already returned
the first resolved images of two asteroids,
951 Gaspra and
243 Ida,
while in transit to Jupiter. It has also returned pictures of
the impact
of Comet SL9 onto Jupiter from its
unique vantage
point.

Efforts to unfurl the stuck High Gain
Antenna (HGA) have essentially been abandoned.
With its Low Gain Antenna
Galileo transmits data at about 10 bits per second.
JPL has developed a
backup plan using enhancements of the receiving antennas in the
Deep
Space Network and data compression (JPEG-like for images,
lossless
compression for data from the other instruments) on the
spacecraft. This
should allow Galileo to achieve approximately 70% of its
original
science objectives with the much lower speed Low Gain Antenna.
Long term
Jovian weather monitoring, which is imagery intensive, will
suffer the
most.

launched April 1990;
fixed December 1993.
HST can provide pictures and spectra over a long period of
time.
This provides an important extra dimension to the higher
resolution data from the planetary probes. For example, recent
HST data show
that Mars
is colder and drier than during the Viking missions; and HST
images of
Neptune
indicate that its atmospheric features change rapidly.

now investigating the
Sun's polar regions (European Space
Agency/NASA).
Ulysses was launched by the Space Shuttle Discovery in October
1990.
In February 1992, it got a gravity boost from Jupiter
to take it out of the plane of the
ecliptic.
It has now completed its main mission of surveying both of the
Sun's
poles.
Its mission has been extended for another orbit so that it can
survey
the Sun's poles near the maximum of the sunspot cycle, too.
Its aphelion is 5.2 AU, and,
surprisingly, its
perihelion is about 1.5 AU-- that's right, a solar-studies
spacecraft
that's always further from the Sun than the Earth is!
It expected to provide a much
better understanding of the Sun's magnetic field and the
solar wind.

After its November 1, 1994, launch, NASA's Wind satellite will
take up a vantage point between the Sun and the Earth, giving
scientists a unique opportunity to study the enormous flow of energy
and momentum known as the solar wind.

The main scientific goal of the mission is to measure the mass,
momentum and energy of the solar wind that somehow is transferred into
the space environment around the Earth. Although much has been
learned from previous space missions about the general nature of this
huge transfer, it is necessary to gather a great deal of detailed
information from several strategic regions of space around the Earth
before scientists understand the ways in which the planet's atmosphere
responds to changes in the solar wind.

The launch also marks the first time a Russian instrument will
fly on an American spacecraft. The Konus Gamma-Ray Spectrometer
instrument, provided by the Ioffe Institute, Russia, is one of two
instruments on Wind which will study cosmic gamma-ray bursts, rather
than the solar wind. A French instruments is also aboard.

At first, the satellite will have a figure-eight orbit around the
Earth with the assistance of the Moon's gravitational field. Its
furthest point from the Earth will be up to 990,000 miles (1,600,000
kilometers), and its closest point will be at least 18,000 miles
(29,000 kilometers).

Later in the mission, the Wind spacecraft will be inserted into
a special halo orbit in the solar wind upstream from the Earth, at the
unique distance which allows Wind to always remain between the Earth
and the Sun (about 930,000 to 1,050,000 miles, or 1,500,000 to
1,690,000 kilometers, from the Earth).

The Near Earth Asteroid
Rendezvous (NEAR) mission promises to answer fundamental questions
about the nature of near-Earth objects such as asteroids and
comets.

Launched on 1996 February 17 aboard a Delta 2 rocket, the NEAR
spacecraft should arrive in orbit around asteroid 433 Eros in early
January 1999. It will then survey the rocky body for a minimum of one
year, at altitudes as close as 15 miles (24 kilometers). Eros is one
of the largest and best-observed asteroids whose orbits cross Earth's
path. These asteroids are closely related to the more numerous "Main
Belt" asteroids that orbit the Sun in a vast doughnut-shaped ring
between Mars and Jupiter.

Launched with a Delta II expendable vehicle from Cape Canaveral,
Fla., on November 7 1996, the spacecraft is now in orbit around Mars.
The spacecraft circles Mars once every two hours, maintaining a
"sun synchronous" orbit that will put the sun at a standard angle
above the horizon in each image and allow the mid-afternoon lighting
to cast shadows in such a way that surface features will stand out.
The spacecraft will carry a portion of the Mars
Observer instrument payload and will use these instruments to
acquire data of Mars for a full Martian year, the equivalent of about
two Earth years. The spacecraft will then be used as a data relay
station for signals from U.S. and international landers and
low-altitude probes for an additional three years.

The Mars Pathfinder (formerly known as the Mars Environmental Survey,
or MESUR, Pathfinder) is the second of NASA's low-cost planetary
Discovery missions. The mission consists of a stationary lander and a
surface rover known as Sojourner. The mission has the primary
objective of demonstrating the feasibility of low-cost landings on and
exploration of the Martian surface. This objective will be met by
tests of communications between the rover and lander, and the lander
and Earth, and tests of the imaging devices and sensors.

The scientific objectives include atmospheric entry science,
long-range and close-up surface imaging, with the general objective
being to characterize the Martian environment for further exploration.
The spacecraft will enter the Martian atmosphere without going into
orbit around the planet and land on Mars with the aid of parachutes,
rockets and airbags, taking atmospheric measurements on the way down.
Prior to landing, the spacecraft will be enclosed by three triangular
solar panels (petals), which will unfold onto the ground after
touchdown.

Mars Pathfinder was launched 1996 December 4 and landed
successfully on Mars on 1997 July 4.

Saturn
orbiter and Titan atmosphere probe.
Cassini is a joint
NASA/ESA project designed to accomplish an exploration of the Saturnian
system with its Cassini Saturn Orbiter and Huygens Titan Probe. Cassini
was launched aboard a Titan IV/Centaur 1997 Oct 15.
En route to Saturn, Cassini will first execute two gravity assist flybys
of Venus, then one of Earth, and then one of Jupiter (a "VVEJGA" trajectory).
It will arrive at Saturn on 2004 July 1.
Upon arrival, the Cassini spacecraft performs several maneuvers to achieve an
orbit around Saturn. Near the end of this initial orbit, the Huygens
Probe separates from the Orbiter and descends through the atmosphere of
Titan. The Orbiter relays the Probe data to Earth for about 3 hours
while the Probe enters and traverses the cloudy atmosphere to the
surface. After the completion of the Probe mission, the Orbiter
continues touring the Saturnian system for three and a half years. Titan
synchronous orbit trajectories will allow about 35 flybys of Titan and
targeted flybys of Iapetus,
Dione and
Enceladus. The objectives of the
mission are threefold: conduct detailed studies of Saturn's atmosphere,
rings and magnetosphere; conduct close-up studies of Saturn's
satellites, and characterize Titan's atmosphere and surface.

An earlier plan for an asteroid fly-by on the way out similar to the
highly successful Galileo fly-bys of
Ida and Gaspra
was scrapped in order to reduce costs.

One of the most intriguing aspects of Titan
is the possibility that its
surface may be covered in part with lakes of liquid hydrocarbons that
result from photochemical processes in its upper atmosphere. These
hydrocarbons condense to form a global smog layer and eventually rain
down onto the surface. The Cassini orbiter will use onboard radar to
peer through Titan's clouds and determine if there is liquid on the
surface. Experiments aboard both the orbiter and the entry probe will
investigate the chemical processes that produce this unique atmosphere.

Lunar Prospector, the first NASA mission to the Moon in almost 30 years,
was launched Jan 6th, 1998. Within a month
it will begin returning answers to long-standing questions about the
Moon, its resources, its structure and its origins.
(Welcome to the Moon, Lunar Prospector home page);
more from NSSDC

Scheduled for launch in February 1999,
Stardust will fly close to a comet and, for the first time ever, bring
material from the comets coma back to Earth for analysis by scientists worldwide.
Scheduled to fly-by Comet Wild-2 in 2004, return to Earth in 2006.

Future Missions

As part of NASA's Ice and Fire
Preprojects, planning has begun on a mission to send a spacecraft to
Europa to measure the thickness of the surface ice and to detect an
underlying liquid ocean if it exists. Using an instrument called a radar
sounder to bounce radio waves through the ice, the Europa Orbiter
sciencecraft would be able to detect an ice-water interface, perhaps as
little as 1 km below the surface. Other instruments would reveal details
of the surface and interior processes. This mission would be a precursor
mission to sending "hydrobots" or remote controlled submarines that
could melt through the ice and explore the undersea realm.

(was Pluto Express and before that Pluto Fast Fly-by) a small, fast, relatively
cheap initial
look at the as yet unvisited Pluto.
Possible launch in 2001 (if a 1998 new start is
authorized). Calls for launch of two spacecraft weighing less
than 100 kg
using Titan IV/Centaur or Proton (possibly with additional solid
kick stages) in 2001 and encounters with Pluto and
Charon
around 2006-8 (depending on trajectory choice).
Flybys would be at 12-18 km/second; data would be
recorded onboard the probes during the short encounters and
returned to Earth slowly (due to low power, small antenna sizes,
and large distances) over the next year or so. Russian "Drop
Zond" probes to sample the atmosphere may be included as well.

Science objectives include characterizing global geology and
geomorphology of Pluto and Charon, mapping both sides of each
body, and characterizing Pluto's atmosphere (the atmosphere is
freezing out as Pluto moves away from the Sun, so launching
early and minimizing flight time is critical for this
objective). The 7 kilogram instrument package might include a
CCD imaging camera, IR mapping spectrometer, UV spectrometer,
and radio science occultation experiments.

The PFF spacecraft would be highly a miniaturized descendant of
the present class of outer solar system platforms, breaking the
trend of increasingly complex and expensive probes such as
Galileo and Cassini.

There's an article about PFF by its designers in the Sep/Oct 1994
issue of The Planetary Report, the
bimonthly newsletter from The Planetary Society.

Muses-C
The Japanese-managed Muses-C mission will
collect and return to Earth a sample from an asteroid.

This innovative mission will use new flight technology,
including solar electric propulsion, to send a spacecraft to
asteroid 4660 Nereus and deliver a JPL-developed rover, which
measures about the size of a shoebox, to the asteroid's surface.
The Muses-C spacecraft will also fire explosive charges
into the asteroid, collect the samples that are ejected from the
impacts, and return the samples to Earth in a capsule for
laboratory analysis. The mission is scheduled for launch in
2002.